Preparation And Performance Study Of Pt And Pd Electrocatalysts Supported By Cation Vacancy CoFe-LD

The electrocatalysis is a practicable solution to solve the current energy crisis and environmental problems.Layered bimetallic hydroxides（LDHs）have been widely used as an excellent electrocatalyst.However,conventional LDHs suffer from problems such as single catalytic direction and poor stability,which lead to great limitations in their applications for pollutant degradation/conversion and multifunctional catalytic energy conversion.Therefore,it is urgent to develop novel LDHs with high performance,stability and multifunctionality.Currently,the optimization of primitive LDHs with single function and poor stability by externally introducing active sites to form catalysts in the form of active site-catalyst carriers is considered as an effective strategy to improve the catalytic orientation of LDHs.Pd is widely considered to play a key role in dehalogenation and hydrogenation catalytic reactions because of its excellent active hydrogen atom（H*）generation ability.Pt,as one of the most common electrocatalysts,has convincing performance in hydrogen release reaction（HER）and oxygen reduction reaction（ORR）catalytic processes.However,conventional Pd-based catalysts often suffer from poor H*selectivity and easy clustering;Pt-based catalysts suffer from low utilization and poor stability.Therefore,it is crucial to develop loaded Pd-based and Pt-based LDHs with excellent performance,high stability and multifunctional catalysis to solve the above problems.In this paper,novel LDHs（Co Fe _V-LDH,Pd@Co Fe _V-LDH,Pt@Co Fe _V-LDH）with excellent dechlorination and hydrogenation performance,and triple-function catalytic energy conversion were prepared by Zn-doped Co Fe-LDHs as catalyst precursors through alkali etching and photoreduction techniques,respectively.Their morphology,physicochemical properties and electrochemical performance were characterized by various physical and chemical means,and their applications in halogenated organic compounds conversion,full water splitting and zinc air batteries were further investigated.（1）The Zn-doped Co Fe-LDH grown on nickel foam was formed by hydrothermal synthesis and used as precursor,the defects were fabricated by alkali etching,photoreduction was performed in Pd Cl₂hydrochloric acid solution to anchor Pd within the vacancies generated by alkali etching,and the assembled catalyst（Pd@Co Fe _V-LDH/NF）was used as a cathode for the dechlorination and hydrogenation reaction.The prepared optimal sample achieved 95.46%conversion of 10 ppm2,4-dichlorophenol at a very low Pd loading(0.387 mg cm^-2)under an applied current of10 m A and exhibited excellent cycling stability（91.87%for 5 cycles）.Pd@Co Fe _V-LDH/NF possessed good p H adaptability（4～11）,anion tolerance(4 m M Cl^-,NO₃^-,NO₂^-,CO₃^2-)and halogenated phenol pervasiveness.From theoretical calculations,the Pd@Co Fe _V-LDH catalyst with a suitable degree of etching possesses high selectivity for H*（HER Free energy=-1.23 e V）and good adsorption energy for 2,4-dichlorophenol(E_ads=-2.88 e V).（2）The Zn-doped Co Fe-LDH was formed by hydrothermal synthesis and used as a precursor to fabricate defects（Co Fe _V-LDH）by alkali etching,and the catalyst Pt@Co Fe _V-LDH was assembled by photoreduction in aqueous H₂Pt Cl₆solution,which allowed to anchor Pt within the vacancies generated by alkali etching.Co Fe _V-LDH has superior performance in the oxygen release reaction（OER）,only require an overpotential of 241 m V to reach a current density of 10 m A cm^-2in 1 M potassium hydroxide solution.After anchoring Pt within vacancies,the long cycle of Pt@Co Fe _V-LDH remained 99.1%after 36 hours for OER.Pt@Co Fe _V-LDH possesses fast HER kinetics(10 m A cm^-2,72 m V overpotential),fast electron transfer capability(Tafel slope 65 m V dec^-1)and stable long cycling（24 h96.1%）in 1 M potassium hydroxide solution.Not only that,Pt@Co Fe _V-LDH possesses excellent ORR half-wave potential(E_1/2=0.819 V)and efficient Pt utilization(TOF:0.2771 S^-1)in 0.1 M potassium hydroxide solution.The full water splitting device consisting of Co Fe _V-LDH as anode and Pt@Co Fe _V-LDH as cathode exhibited excellent capacity(only 1.57 V for 10 m A cm^-2)and stability（99%for 8 h）.The liquid Zn air battery device consisting of a Zn plate as the anode and a carbon paper coated with 1 mg Pt@Co Fe _V-LDH as the cathode also exhibited an impressive performance(200 m W cm^-2peak power density)and stability.